1. Field of the Invention
The invention relates to a motor control apparatus, and more particularly, a motor control apparatus that uses an electrical angle in which an electrical angle of 360° is set smaller than a mechanical angle of 360°.
2. Description of the Related Art
A motor control apparatus is provided in a vehicle such as a hybrid vehicle or an automobile having an electric motor, or other electrical equipment having a motor. A rotation angle detecting apparatus that detects the rotation angle of the motor is used for this kind of motor control apparatus.
For example, Japanese Patent Application Publication No. 2009-77481 (JP-A-2009-77481) describes technology that uses a resolver as a rotation detecting sensor, and directs an R/D (resolver/digital) converter that converts the output of that resolver into a digital value to increase or decrease a count value.
The motor is basically controlled using the electrical angle that changes according to the number of pairs of poles. For example, in a motor with one pair of poles, the electrical angle matches the mechanical angle. However, in a motor with two pairs of poles, the electrical angle will the change from 0° to 360° twice for each one time that the mechanical angle changes from 0° to 360°. That is, in a motor with two pairs of poles, it is uncertain whether an output of an electrical angle from 0° to 360° corresponds to a mechanical angle of 0° to 180° or a mechanical angle of 180° to 360°.
In recent years, demand has grown for increased torque, reduced size, and smoother control in motors provided in vehicles, so it is possible that the number of pairs of poles in motors will increase from two to four or five, for example. In this case, a resolver with a multiplication factor of angle of 2, 4, or 5 (also denoted as 2×, 4×, or 5×) is normally used. The multiplication factor of angle is the ratio of the angle of one cycle of resolver output (normally the electrical angle θe) to the actual mechanical angle θm of the resolver. That is, the mechanical angle θm=the electrical angle θe/multiplication factor of angle N. Incidentally, the multiplication factor of angle is the factor not the angle, so the multiplication factor of angle may also simply be referred to as the multiplication factor in this specification.
However when a rotation angle sensor such as a resolver is made smaller or the multiplication factor of angle is increased, problems in machining accuracy may result in characteristic variation that corresponds to the multiplication factor even when the electrical angle is the same. When there is such variation in the characteristic of the sensor, the sensor is preferably used after first correcting the output such that the ideal characteristic is obtained.
FIG. 20 is a graph showing a correction of the characteristic of a resolver having a multiplication factor of angle Nx. Referring to FIG. 20, the horizontal axis represents the rotation angle of the resolver, and the vertical axis represents a count value that corresponds to the rotation angle. When the characteristic of the resolver is converted as it is to a digital value, the output value deviates from the ideal value. The rotation speed and the like can be correctly calculated by correcting this output value so that it matches the ideal value.
This deviation of the output value is deviation that corresponds to the positions between a mechanical angle of 0° and 360° due to machining accuracy or the like of the sensor. In other words, even if the electrical angle is the same value, the amount of deviation will differ depending on the position of the mechanical angle to which that electrical angle corresponds, so the correction value must also be changed. More specifically, when an electrical angle of 0° to 360° is a multiplication factor of angle 2×, the correction must be made after first confirming whether the output value (i.e., the electrical angle) corresponds to a mechanical angle between 0° and 180° or a mechanical angle between 180° and 360°. With a multiplication factor of angle 5×, the electrical angle indicated by the current output value could correspond to any one of five mechanical angles.
Incidentally, two-phase encoder output is used as the output of the R/D converter that converts the output of the resolver into a digital value. This two-phase encoder output includes an A-phase signal, a B-phase signal, and a Z-phase signal. The A-phase signal and the B-phase signal are signals that include pulses of a number that corresponds to the rotation angle. A phase difference is provided on the rising edge and the falling edge of the pulse between the A-phase signal and the B-phase signal, so it is possible to ascertain whether rotation is positive or negative by the phase relationship between the A-phase signal and the B-phase signal. Also, the Z-phase signal is a signal that is output once for every one rotation of electrical angle. This kind of interface is widely used in the field of motor control. With a typical two-phase encoder counter that counts by receiving two-phase encoder output, the electrical angle can be recognized but the mechanical angle cannot.
Also, there is a need for the motor itself to be made smaller, so the effects from unbalanced winding of the winding (i.e., coil) and the like increases, which tends to cause uneven rotation. In particular, at low rotation speeds, occupants are likely to feel torque ripple, so it is preferable to perform control to cancel out this torque ripple or the like with motor control. However, in this case as well, it is necessary to recognize whether the output value (i.e., the electrical angle) of the rotation detecting sensor corresponds to a mechanical angle of 0° to 180° or a mechanical angle of 180° to 360° before correcting the motor control.